Method and apparatus for determining the absolute value of the flow velocity of a particle-transporting medium

The invention relates to a method for determining the absolute value of the flow velocity (v) of a particle-transporting medium. At least two measurement laser beams (L_i) with linearly independent, non-orthogonal measurement directions (b_i) are emitted. The measurement laser beams (L_i) scattered at particles are detected and one measurement signal (m_i) is generated in each case for each measurement laser beam (L_i). The measurement signals (m_i) are evaluated, wherein absolute values of velocity components (v_i) are ascertained as projections of the flow velocity (v) on the respective measurement directions (b_i), wherein a solid angle region is ascertained for the prevalent direction of the flow velocity (v) and signs assigned to this solid angle region are chosen for the individual velocity components (v_i), and wherein the absolute value of the flow velocity (v) is determined using the ascertained absolute values of the velocity components (v_i) and using the chosen signs for the velocity components (v_i).